Method of producing all skin rayon



United States Patent METHOD oF PRODUCING ALL SKIN RAYON Byron A. Thumm, Prospect Park, Pa., assignor to American Viscose Corporation, Philadelphia, Pa., a corporation of Delaware 7 Claims. or. 18-54) This invention relates to the production of shaped bodies of regenerated cellulose from viscose and more particularly to filaments and fibers of regenerated cellulose from viscose. I

In the conventional methods of producing shaped bodies of regenerated cellulose from viscose, a suitable cellulosic material such as purified cotton linters, wood pulp, mixtures thereof, and the like is first converted to an alkali cellulose by treatment with a caustic'soda solution and after shredding the treated cellulose material, it is allowed to age. The aged alkali cellulose is then converted to a xanthate by treatment with carbon disulfide. The cellulose xanthate is subsequently dissolved in a caustic soda' solution in an amount calculated to provide a viscose of the desired cellulose andalkali content. After filtration, the viscose solution is allowed to ripen and is subsequently extruded througha shaped orifice into'a suitable coagulating and regencratingbath. 1

In the production of shaped bodies such as filaments, the viscose solution is extruded through a spinneret into a coagulating and regenerating bath consisting of an aqueous acid solution containing zinc sulfate. The filament may subsequently be passed through a hot aqueous bath where it is stretched to improve its properties such as tensile strength. The, filament. may then be passed through a dilute aqueous solution of sulfuric'acid and sodium sulfate to complete the regeneration of the cellulose, in'case .it is not completely regenerated upon leaving the stretching ,stag e. The filament is subsequently subjected/to washing, purification, bleaching, possibly other treating operations and drying, being collected 1 either before or after thesetreatments. J

Patented June 24, 1958 2 I. i 7 position of the spinning bath is maintained within certain composition limits which will be defined hereinafter.

The most readily distinguishable characteristic as com pared to conventional filaments include a smooth,noncrenulated surface and the filaments consist, entirely of skin. All of, the monoaminopyridines are satisfactory, that is, 2-, '3- and 4-aminopyridine'may be employed,

Where the monoaminopyridine, isyto be added tow the viscose, the amount which is incorporated in viscose must beat least about 0.75% by weight of the cellulose in the viscose and may vary up to about 2.5% to 3%, preferably, the amount varies from about 1% to 2% Lesser, amounts do not result. in the production of products consisting entirely of skin and greater amounts affect adversely the physical properties of the products. Amounts within the preferred range are most effective in enhancing the characteristics and properties of the products. The mono aminopyridine may be added at any desired stage in the production of the viscose such as in the preparation of the refined wood pulp for the, manufacture of viscose, before or during the shredding of the alkali cellulose, to the xanthated cellulose while it is being dissolved in the caustic solution or to the viscose solution before or after filtration. The monoarninopyridine is preferably added after the cellulose xanthate has been dissolved in the caustic solution and prior to filtration.

The viscose may contain fromabout 6% to about 8% cellulose, the particular source of the cellulose being selected for the ultimate use of the regenerated cellulose product. The caustic soda content may be from about 4% to about 8% and the carbon disulfide content may be from about 30% to about 50% based upon the weight of the cellulose. The modified viscose, that is, a'viscose containing the small amount of monoaminopyridine, may have a salt test above about 7 and preferably above about 9 at the time of spinning or extrusion. 1 In order to obtain the improvements enumerated here- 'inbefore, it is essentialthat the composition of the spinning bath be maintained within a well defined range. -The baths results in the production of yarns of improved prop- ,erties such as high tenacity, high abrasion resistance, high The filaments asformed by the conventional methods consist of a skin or outer shell portion and a core portion with'a sharp line of 'demarkation between the two. The cross-section of the'filaments exhibits a very irregular or crenulated exterior surface when even small amounts of zinc salts or certain other polyvalent. metal salts are present in the spinning bath. The skin and core portions of the filament represent differences in structure and these different portions possess different swelling and stainingcharacteristics, the latter permitting a ready entirely of skin.

fatigue resistance and consisting of filaments composed Generically, and in terms of the industrial art, the spinning bath is a low acid-high zinc spinning bath. The bath should contain from about 10% to. about 25% sodium sulfate and from about 3% to about zinc sulfate, preferably from 15% to 22% sodium sulfate and from 4% to 9% zinc sulfate. Other metal sulfates such as iron, manganese, nickel and the like may be present and may replace some of the zinc sulfate. The temperature of the spinning bath may vary from about 25 C. to about 80 C., preferably between about C. and about 70 C.

identification of skin and core.. The sharply irregular and crenulated surface structure has a relatively low abrasion resistance and readily picks up foreign particles such as dirt. Although the core portion possesses a relatively high tensile strength, it has a low abrasion resistance-and a lowfiexelife, issubject to fibrillation and v is relatively stiff. I 4 v a 'It has nowbeen discovered that the presence of'small amounts of a monoarninopyridine in the viscose,,in the spinning bath, orinboth the viscose, andthe bath-results in the production of shaped bodies of regenerated cellulose. such as' filaments, films, sheets and the like composed of all skin and having improved properties and characteristics providing that the amount of monoaminopyridine is maintained within certain limits and the com- In the production of the all skin type filaments,-the temperature of the spinning bath is not critical, however, as is well known in the conventional practice in the art,

certain of the physical properties such as tensile strength vary directly with the temperature of the spinning bath.

Thus, in the production of filaments for tire cord purposes in accordance with the method of thisjinvention,

.. the spinning bath is preferably maintained at attemperature between about 55 C. and 65 C. so tain the desired high tensile strength,

The acid content of the spinning bath is balanced against the composition of the viscose. The lower limit of the acid concentration, as is well known in the art, is just above the slubbing point, that is, the concentration at which small slubs of uncoagulated viscose appear in the strand as it leaves the spinning bath. For come as to obmaintained constant.

mercialoperations, the acid concentration of the spinning bath is generally maintained about 0.4% to 0.5% above the slubbing point. For any specific viscose composition, the acid concentration of the spinning bath must maintained above the slubbing point and below the point at which the neutralization of the caustic of the "viscose: is sufliciently rapid to form a filament havinga skinsand core.

There is a maximum acid concentration for any specific viscose compositionybeyond which the neutralization is sufliciently rapid to produce filaments having a skin and core. For example, in general, the acid concentration of thespinning baths which are. satisfactory for the production of the all skin products from a 7% cellulose, 6% causticwiscose and containing monoarninopyridine lies between about 6% and ab'out"8.4% The acid concentration may be increased as the amount of monoaminopyridine is increased and also as the salt test of the vis- --cose is increased. There is an upper limit, however, for

about 36% (based on the weight of cellulose) carbon disulfide, 1% (based on the weight of cellulose) of monoaminopyridine and having a salt test of about 9 when extruded into spinning baths containing 16 to 20% sodium sulfate, 4 to 8% zinc sulfate and sulfuric acid not more than about 8.5 results in the production of all skin filaments. f Lesser amounts of sulfuric acid may be "employed. Greater amountsof sulfuric acid result in the production of products having skin and core. A loweringyof the amount of monoatninopyridine, the lowering of the caustic soda content or the lowering of the salt test of theviscosereduces the maximum permissible acid concentration for the. production of all skin filaments. It has been determined that the maximum concentration of acid which is permissible for the production of all skin products isabout 9%. l 9 g The presence of the monoaminopyridine in the viscose retards the coagulation and, thereforefthe amount of monoaminopyridine employed must be reduced at high spinning speeds. Thus, for optimum physical character-- istics of an all skin yarn formed froma viscose as above and at a spinning speed of about 50 meters per minute, the 'adduct is employed inamounts within the lower portion of the range, for example, about 1%. The determination of the specific maximum and optimum concentration of acid for any specific viscose, spinning bath and spinning speed is a matter of simple experimentation for those" skilled in the art. The extruded viscose must, of a course, be immersedor maintained in the spinning bath fora period sutficient to elfect relatively complete coagulation o'f the viscose, that is, the coagulation must be sufficient so that the filaments willnot adhere to each other a's they are brought together and withdrawn from the bath v In the production of' filaments for. such purposes as the fabrication of tire cord, the filaments are preferably stretched after removal 'fromthe initial coagulating and regenerating bath. From the initial spinning .bathpthe filaments may be passed through a hotaqueous bath 'which may consist of hot water or a dilute acid solution I and' rnaybe stretched from about 170% to 120%, preferably between 85%a'nd 100% Yarns for other textile purposesmay be stretched as low as 20%. The precise amount of stretching willbe dependent upon the desired "tenacity and other properties and the specific type of product being produced. It is to be understood that the 4 invention is not restricted to. the production of filaments and yarns but it is also applicable to other shaped bodies such as sheets, films, tubes and the like. The filaments may then be passed through a final regenerating bath which may contain from about 1% to about 5% sulfuric acid and from about 1% to about 5% sodium sulfate with or without small amounts of Zinc sulfate if regeneration has not previously been completed.

The treatment following the final regenerating bath, or the stretching operation where regeneration has been complcted, may consist of a washing step, a desulfurizing step, the application of a finishing or plasticizing material and drying before or after collecting, or may include other desired and conventional steps such as bleaching and the like. The treatment after regeneration will be dictated by the specific type of shaped body and the proposed use thereof.

Regenerated cellulose filaments prepared from viscose containing the small amounts of monoaminopyridine and spun in the spinning baths of limited acid content have a smooth or non-crenulated surface and consist substantially entirely of skin. Because of the uniformity of structure throughout the filament, the swelling and staining characteristics are uniform throughout the crosssection of the filament. Filaments produced pursuant to this invention and consisting entirely ofskin have a high toughness and a greater flexing life than filaments as produced according to prior methods which may be attributed by the uniformity in skin structure throughout the filament. Although the twisting of convenional filaments, as in the production of tire cord, results in an appreciable loss of tensile strength, there is appreciably less loss in tensile strength in the production of twisted cords from the filaments consisting entirely of skin. Filaments prepared from viscose containing the monoaminopyridine. have superior. abrasion and fatigue re sistance characteristics. and have a high flex-life as compared to normal regenerated cellulose filaments. Such filaments are highly satisfactory for the production of cords for .the reinforcement of rubber products such as pneumatic tire. casings, but the filaments are .not restricted to such uses andmay be used for other textile applications.

Like improvements in the characteristics and properties of the products are also obtained by incorporation of the monoaminopyridine in "the spinning bath in place of adding it to the viscose." Itis essential thatthe composition of the spinning bath, partcularly the acid concentration be maintained within the limits set forth hereinbefore. In order to produce products consisting of all skin, the amount of monoaminopyridine dissolved in the spinning bath must be at least about 0.01% by weight and is preferably maintained between about 0.05% and about 0.1 The upper limit of the amount added to the spinning bath is dependent upon economic considerations since amounts exceeding about 0.1% are not more effective in improving the properties of the products.

It is obvious that monoaminopyridine may be added to both the viscose and the spinning bath, if desired. In such instance, it is'also essential to maintain the amounts of the monoaminopyridine in the viscose and in the spinning bath, and the composition of the spinning bath within the statedlimits. The all skin products of improved properties are obtained only when the spinning operation in the presence of monoaminopyridine is carried out within the spinning bath composition as set forth hereinbefore. I a Y The invention may-be illustrated by reference to the preparationof regenerated cellulose filaments from a viscose containing about 7 cellulose, about 6.5% caustic soda, and having a total carbon disulfide content of about 36% based on the weight of the cellulose. The

viscose solutions were prepared byxanthating alkali 'cellulose by the introduction of 36% carbon disulfide based On the weight of the cellulose and churning for about 2% hours. The viscose was then allowed to ripen for about 30 hours at 18 C. In those instances where the modifier was incorporated in the viscose, the desired amount of monoaminopyridine was added to the solution and mixed for about /2 hour before allowing the viscose to ripen.

Example 1 Approximately 1% 2-aminopyridine (based on the weight of the cellulose) was added to andincorporated in the viscose as described above. The viscose employed in the spinning of filaments had a salt test of 9.1. The viscose was extruded through a spinneret to form a 200 denier, 120 filament yarn at a rate of about 43 meters per minute. The coagulating and regenerating bath was maintained at a temperature of about 60 C. and contained 8.3% sulfuric acid, 8% zinc sulfate and 17% sodium sulfate. The yarn was stretched about 74% while passing through a hot water bath maintained at 95 C. The yarn Was collected in a spinning box, washed free of acids and salts and dried.

The individual filaments have a smooth, non-crenulated exterior surface and consist entirely of skin, no core being detectable at high magnification (e. g. 1500 The filaments of a control yarn spun with the same viscose but without the addition of the modified agent and spun under the same conditions, exhibit a very irregular and serrated surface and are composed of about 60% to 70% skin and the balance core with a sharp line of demarkation between the skin and core. Other physical properties are set forthin the table which follows the examples.

Example 2 A viscose solution as' described above (no modifier added) having a salt test of 9.2 was spun into a 210 denier, 120 filament yarn by extrusion into a spinning bath containing 8.1% sulfuric acid, 8% zinc sulfate, 19% sodium sulfate and 0.05% 2-aminopyridine. The bath was maintained at 60 C. and the extrusion rate was about 22 meters per minute. The filaments were passed through a hot water bath maintained at about 95 C. and stretched about 82%. The yarn was collected in a spinning box, washed free of acid and salts and dried.

The filaments have a smooth, non-crenulated surface and consist entirely of skin while control filaments have a very irregular and serrated surface and consist of about 60% to 70% skin and the balance core with a sharp line of demarkation between the skin and core. Other physical characteristics are set forth in the table which follows the examples.

Example 3 To a viscose as described above, there was added 1% Z-aminopyridine. The viscose had a salt test of 9.2 and was spun into a 210 denier, 120 filament yarn by extrusion into a spinning bath containing 8.3%* sulfuric acid, 8% zinc sulfate, 17% sodium sulfate, and about 0.05% Z-aminopyridine. The bath was maintained at 60 C. and the extrusion rate was about 22 meters per minute. The filaments were subsequently passed through a hot water bath at 95 C. and stretched about 82%. The yarn was collected in a spinning box, washed free of acids and salts and dried.

The individual filaments were readily distinguishable from control filaments in that they have a smooth, noncrenulated surface and consist entirely of skin while the control face and consist of about 60% to 70% skin and the balance core with a sharp line of demarkation between the skin and the core. Other physical properties are set forth in the table which follows the examples.

Example 4 filaments have a very irregular and serrated sur-- the swelling amounting to then in one or more baths composed of 10% As a control for the foregoing examples, a viscose solution, prepared as described above, having a salt test be determined.

of 9.2 was spun into a210 denier, 120 filament yarn by extrusion into a bath containing 7.9% sulfuric acid, 8% zinc sulfate and 20% sodium sulfate. The bath was maintained at a temperature of about 60 C. The extrusion rate was about 22 meters per minute. The'water bath was maintained at a temperature of about 95 C. and the filaments were stretched 82% while passing through the hot water. The yarn was collected in a spinning box, washed free of acid and salts and dried.

The individual filaments have a very irregular and serrated surface and consist'of about 60% to 70% skin and the balance core with a sharp line of demarkation between the skin and the core. Other characteristics are set forth in the table which follows:

Although the tenacity and elongation are the only properties set forth, they have been chosen because of the ease and simplicity with which such properties may In some instances, products made'in accordance with this invention do not exhibit large or great improvements in tenacity and elongation, however,

the products consist of a smooth-surfaced, all skin structure and possess improved abrasion resistance, flex-life and other properties as disclosed hereinbefore.

One of the properties of viscose rayon which has limited its uses is its relatively high cross-sectional swelling when wet with water, this swelling amounting to from about 65% to about for rayon produced by conventional methods. Rayon filaments produced in accordance with the method of this invention have an appreciably lower cross-sectional swelling characteristic, from about 45% to about 60%.

The monoaminopyridine may be added to any desired viscose such as those normally used in industry, the specific viscose composition set forth above, being merely for illustrative purposes. be added at any' desired stage in the production of the viscose and may be present in the cellulosic raw material although it may be necessary to adjust the amount present to produce a viscose having the proper proportions of the adduct at the time of spinning.

The term skin is employed to designate that portion of regenerated cellulose filaments which is permanently stained or dyed by the following procedure: A microtome section of one or more of the filaments mounted in awax block is taken and mounted on a slide with Meyers albu- 1 min fixative. After dewaxing in xylene, the section is placed in successive baths of 60% and 30% alcohol for a few moments each, and it is then stained in 2% aqueous solution of Victoria Blue BS conc. (General Dyestuffs Corp.) for 1 to 2 hours. At this point, the entire section is blue. By rinsing'the section first in distilled water and dioxane for a period varying from 5 to 30 minutes depending on the particular filament, the dye is entirely removed from the core, leaving it restricted to the skin areas.

While preferred embodiments of the invention have I been disclosed, the description is intended to be illustraa tive and it is to be understood that changes and variations may be made without departing from the spirit and scope of the invention as defined by the appended claims.

I claim:

1. In a method of producing shaped bodies of regener ,ated cellulose consisting substantially entirely of skin,

The monoaminopyridine may water and 7 the step which comprises extruding viscose into an aqueous spinningbath in the presence of a smallamount of monoaniinopyridine, the bath containing from about 10% to 25% sodium sulfate, from about 3% to 15% zinc sulfate and sulfuric acid, the sulfuric acid content of the spinning bathexceeding the slubbing .point but, not exceeding about 9%.

2. In-a method of producing shaped bodies of regenerated cellulose consisting substantially entirely of skin,

the step which comprises extruding viscose containing from about 0.75% to about 2.5% of a monoaminopyridine, based on the weight of thecellulose, into an aqu'eousspinning :bath containing from about 10% to 25 sodium sulfate, :from about 3% to 15 zinc sulfate and sulfuric acid, the sulfuric acid content of the spinning bath exceedingthe slubbing point but not exceeding about 9%.

'3. In a method of producing shaped bodies of regenerated cellulose consisting substantially entirely of skin,

the step which comprises extruding viscose into an aqueous spinning bath containing from about 10% to 25% sodium sulfate, from about 3% to 15 %'zinc sulfate, at least about 0.01% a monoarninopyridine and sulfuric acid, the sulfuric acid contentofthe spinning bath exceeding the slubbing point but not exceeding about 9%.

4. The method of producing shaped bodies of regenerated cellulose consisting substantially entirely of skin which comprises adding to and incorporating in a viscose from about 0.75% to about 2.5% of a monoaminopyridine, the, amount being based upon the weight of the cellulose, and extruding the viscose into an aqueous spinning bath containing from about 10% to 25% sodium sulfate, from about 3% to 15% zinc sulfate and sulfuric acid, the sulfuricacid content of the bath exceeding the slubbing point but not exceeding about 9%.

5. The method of producing shaped bodies of regenerated cellulose consisting substantially entirely of skin which comprises adding to and incorporating in a viscose from about 0.75% to about 2.5% of a monoaminopyridine, the amount being based upon the weight of the cellulose, ripening the viscose to a salt point of not less than 7 and extruding the viscose into an aqueous spinning bath containing from about 16% to 20% sodium sulfate, from about 4% to 9% zinc sulfate and sulfuric acid, the sulfuric acid content of the spinning bath exceeding the slubbing point but not exceeding about 9%.

6. The method of producing shaped bodies of regenerated cellulose consisting entirely of skin which comprises forming an aqueous spinning bath containing in solution from about 10% to 25% sodium sulfate, from about 3% to 15% zinc sulfate, at least about 0.01% of a monoaminopyridine and sulfuric acid, and extruding viscose into the spinning bath, the sulfuric acid content of the bath exceeding the slubbing point but not exceeding about 9%.

7. An aqueous spinning bath for the production of regenerated cellulose products consisting substantially entirely of skin from viscose containing from about 10% to 25 sodium sulfate, from about 3% to 15 zinc sulfate, at least about 0.01% of a monoaminopyridine, and not more than about 9% sulfuric acid.

References Cited in the file of this patent UNITED STATES PATENTS 2,145,527 Polak Jan. 31, 1939 2,312,152 Davis Feb. 23, 1943 2,373,712 Schlosser a Apr. 17, 1945 2,535,044 Cox Dec. 26, 1950 I 2,593,466 MacLaurin Apr. 22, 1952 

1. IN A METHOD OF PRODUCING SHAPED BODIES OF REGENERATED CELLULOSE CONSISTING SUBSTANTIALLY ENTIRELY OF SKIN, THE STEP WHICH COMPRISES EXTRUDING VISCOSE INTO AN AQUEOUS SPINNING BATH IN THE PRESENCE OF A SMALL AMOUNT OF MONOAMINOPYRIDINE, THE BATH CONTAINING FROM ABOUT 10% TO 25% SODIUM SULFATE, FROM ABOUT 3% TO 15% ZINC SULFATE AND SULFURIC ACID, THE SULFURIC ACID CONTENT OF THE SPINNING BATH EXCEEDING THE SLUBBING POINT BUT NOT EXCEEDING ABOUT 9%. 